I wont care about the 5" screen. Dont forget about the zoomfunction and the settings for the fontsize!
The display sounds to be smaller than it is. Of course its more comfortable to read on a bigger screen device, but what i like (and what has been said already) is the mobility of the device, even if you want to read only at home with your reader, who says that it will be like that for the rest of the time?
In the end you have decide on your own which one you are going to buy.